Application 

UPP proppant plug milling tool is designed to drill out and wash over postfracturing proppant plugs in a wellbore.

Design

The tool consists of a mill with integral carburized teeth, a housing, a screw shaft, a lead screw nut, thrust rings and seals. After fracturing, the tool is run into the hole on tubing with reverse circulation on. 
When suspended, the screw shaft is fully extended and the mill is in its lowest position. With the mill landing on the plug, and load, applied to the tool, increasing, coarse pitch of the screw shaft imparts torque to the mill. Hard teeth of the mill destroy proppant crust, while fluid circulates plug debris out of the well.

Pull the string to extend the screw shaft and reapply load until proppant crust is completely drilled out.